The Map That Changed the World (5 page)

Dactylioceras tenuicostatum

W
illiam Smith’s introduction to the curious magic of geology—at a time when it was still a calling more nestled in myth and mystery than in the rigors of scientific discipline—came about in the most prosaic of ways.

It was presaged by domestic tragedy. When William was just eight years old his father, John, suddenly died. He had been something of a skilled mechanic as well as the village blacksmith, and had caught a chill while working outdoors repairing a piece of farm machinery. It was a devastating blow, financially as well as emotionally.

For the next couple of years, until Ann Smith married again, the boy, along with his two brothers, Daniel and John, and a sister, Elizabeth,
*
was largely brought up by his uncle (who, confusingly, was called William too), who also farmed locally.

A romantic might well say that William Smith was almost an orphan. To all intents and purposes, with a father dead and a mother apparently more interested in her new husband than in her child, he was. Life on his uncle’s farm, however, does not appear to have struck him as displeasing. And in any case the farm was itself soon to become symbolically very important in his story—principally because it was substantial enough an establishment to include a dairy.

It was customary in the farms of this part of Oxfordshire for the dairymaid who operated the butter scales (in this case, William’s aunt) to use as a pound weight not an artificial metallic object, as one might buy in a market, but one of any number of curious, rather attractive, sometimes flattened and usually almost circular stones that could easily be found in the quarries nearby.

The farmers took these stones for granted—and why not?—they were merely stones of a certain size, one of those very few conveniences of isolated rural life, to be given no more heed than one might give a clod of earth or a muddy pool. But William, who seems to have had a more curious eye than most, saw on the dairy scales objects that were not ordinary at all. He looked carefully at each one, and realized that there were features about these stones that were uncommonly lovely—and had a meaning that no one else seems to have noticed. No one in the dairy, at the very least.

Some features of the pound stones were quite plain to see. Others required a closer look. When viewed from above, the stones appeared to be round, although in fact some of them were not—some had five sides, but sides that were sufficiently chamfered to give the stone, on cursory inspection, a circular appearance. Then again all the pound stones, whether they were actually round or five-sided, were about four inches across. In cross-section the rounded ones were slightly flattened at the top and bottom, so that each stone would sit on the weighing scale with
out any inclination to roll off. The dairymaids liked this feature: a weighing stone that would stay where it was put.

But whether the stones were flat or indented, round or pentagonal, the Oxfordshire dairymaids found them useful also because they were remarkably uniform in both dimension and mass. Almost all of them weighed in at about twenty-two ounces—which just happened to be what the local dairy managers, in measuring out freshly churned butter for their customers, called a “long pound.”

The five-sided variety was arranged in one of two general kinds of shape, each of which can best be imagined by thinking of an orange, either pressed down flat on a table, or else pressed down on top of a small pebble. Both, in other words, were rounded at the top, but some were totally flat below, while others had a shallow upward indentation at the base.

Oxfordshire pound stones, which the locals still sometimes call Chedworth Buns, are still be found in the plowed fields around Churchill. Close inspection of a good specimen reveals them to be even more complicated than one might suppose. The possession of five sides already suggests some degree of complexity; but in addition their outer surfaces are decorated with a series of quite beautiful filigrees of fine lines and beguiling, elegantly regular patterns.

On the top of each rounded dome, for example, is a small disk, composed of five leaflike plates, which surrounds a tiny circular hole. Down what anyone fondling the stones will surely regard as their rather voluptuously convex sides spread ten ray-like arrangements of what appear to be plates, like armor. The plates are two sizes, large and small—and they are arranged so that one array of the smaller plates alternates with another of the wider plates, five times each. Underneath, at the point where these rays all come together again, like lines of longitude on a globe, there is another hole, quite larger than the one on top. And on some of the five-sided pound stones—but not on the
totally round ones—there is a third hole, somewhat elongated and lozenge shaped, which lies halfway down the curved exterior, right in the center of one of the wider, large-plate rays.

S
uch things had actually first been recognized for what they were—or what they appeared to be—about a century before. It was in Sussex that a local naturalist, wondering about the version of Oxfordshire pound stones that he found in the fields near Brighton, realized that he had seen something very similar-looking that was actually
living
in the rock pools of his local seashore. Wedged into recesses of the pools he had found scores of almost spherical animals, some of them round, some heart-shaped, all covered with sharp spikes—sea urchins, he knew they were called.

Their protective covering of spikes disguised the exoskeletons beneath. But once in a while the naturalist would find on the beach a dead sea urchin, a specimen that had completely lost its spikes. Such a specimen, naked among the pebbles, displayed its eggshell-white exoskeleton perfectly. And this was the vital point of contact—for although the skeletons that were to be found on a Sussex beach were hollow, and fragile, and soap-bubble light, in shape and size and markings they were precisely the same as the solid, heavy stones he had found in the fields nearby.

So this amateur scientist promptly deduced what we today would regard as perfectly obvious—that his pound stones were stones, yes, in that they were solid and made of what were evidently mineral materials, but they were also clearly the remains, or at least precise simulacra, of common sea urchins. They were members of the family known as echinoderms, and of the genus known as
Echinus
, both of which had been named after the Greek and Latin words from which we get
urchin
, which means “hedgehog.”

T
he symmetry and beauty of the sea-urchin-shaped stone that lay on the dairymaid’s butter scales evidently caught the young William Smith’s imagination. It is not difficult to imagine him picking it up, turning it over and over in his hand, examining through a glass its intricate patterns of plates, striations, and whorls. He may well have compared it with pictures of modern sea urchins that he found in his textbooks in the village school, and asked questions of his teacher—an eccentric villager named Billy Watts, who seems to have taught his classes while sitting with a cat on each knee, and who was probably not the source of much enlightenment on the subject.

And, most crucially of all, he may have asked himself questions that more disciplined scientists were even then beginning to puzzle over: Just what was a creature of the oceans doing, preserved—
so strangely!
—as part of a rock? Just how did one solid become so firmly embedded inside another? Just what did such things, such weird phenomena, the encapsulation of objects from the sea deep inside the rocks of Oxfordshire, really mean?

The pound stone, viewed from the side.

Clypeus ploti
—a pound stone—viewed from the top.

It was not long before another such object, just as prosaic, just as lovely, attracted his interest.

Scattered all over the fields around Churchill—but of no interest to the dairymaids—were hundreds of small, thumbnail-size objects, almost spherical, and with a vaguely opalescent sheen to them. They, too, had a subtle, magical beauty: On closer examination, when it was possible to see that their skins had an orange-peel-like texture, with thousands of tiny holes regularly arranged over the surface, their loveliness was even more apparent. They looked a little like acorns; or perhaps William, who might have been taken on school trips to some of the many Roman ruins with which Oxfordshire was littered, might have thought they looked a little like Roman oil lamps. The local farmers, who also spotted the similarity of shape, had long called them lamp shells. William called them “pundibs,” and in his diaries written years later recalled using them as marbles, to play games with his schoolmates.

But like the sea urchins, these lamp-shell stones clearly had no logical place among the arid amassments of rock lying beneath the Oxfordshire fields. For these mimic creatures—if that is what they were—likewise belonged to the ocean. Contemporary, living versions, which could also be found on shallow-sloping sands beside the sea and in the estuaries of rivers, were composed of two small shells, the upper one slightly larger than and curving over the lower, with a small hole at the overlapping edge of the upper shell from which a small gelatinous leg protruded to anchor the shell to the ground.

Once in a while, when shallow sea water washed over the tiny animal, a most extraordinary thing happened: The two shells, which were evidently hinged close to the anchor leg, opened slightly, and from between them flicked a long, curled, rubbery tonguelike organ, which waved among the suspended particles in the water, collected some of the edible morsels that stuck to its surfaces, and was then coiled back smartly between the shells,
which promptly snapped shut. Following this lightning-quick feast the animal then remained static, evidently digesting and nourishing itself on whatever its remarkable feeding limb had managed to collect.

Today we know only too well exactly what the two objects were that the boy so admired, and that so inspired him. The pound stone, an echinoid, was in all probability a species named
Clypeus ploti
, the genus name (from the Latin) given because of its round, shieldlike shape, and its species name given in honor of a long-forgotten Oxfordshire geologist called Robert Plot.
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The marbles that William used in schoolyard play were a type of brachiopod, a terebratulid, and most probably, given its roundness and suitability for games, a small and pretty variety known as
Lobothyris.

But all this begs the original question: What were such sea creatures doing in the middle of a stretch of unenclosed pasture, a hundred miles from the nearest shoreline and (considering the height of the surrounding land above sea level) a good three hundred vertical feet above it? To answer such questions today is quite simple: The shells are just fossils, once organic but now mineralized relics of a time when the rocks that lie beneath the fields of Oxfordshire were themselves being created, thousands of feet beneath a life-rich tropical sea. But in the late eighteenth century, no such theory had ever been even vaguely imagined. When William Smith was being entranced and captivated by the dairymaids’ pound stones, noth
ing about fossils was simple, nothing was universally accepted, nothing was obvious at all.